This invention relates to a speed sensor and more particularly to a rotational speed sensor with improved resolution.
Rotational speed is measured in many different applications, including a starter/generator for aircraft. Existing sensors utilize a magnetic pickup generating a cyclical output based upon passing teeth of a rotating gear. A counter counts a number of clock pulses that are generated during each cycle. In order to avoid overflowing the counter at low speeds, the speed of the clock pulses must be reduced. However, reducing the clock speed reduces the resolution of the speed sensor at higher speeds.
In order to achieve good resolution for an average speed calculation, a very precise position sensor can be used, such as high precision encoder or resolver. However, the cost and size of the resolver or encoder is not always practical. Additionally, the surrounding environment of the sensor may be too harsh for an encoder or resolver.